This invention relates to sailcloth and more particularly to composite materials which are highly durable and may be used, for example, to make very large sails.
Many sails in use today are made from tightly woven continuous filament yarns. Conventional sails are made from flat sheets of tightly woven polyester fabrics. The sheets are cut into panels, and the panels are sewn together using a process called broadseaming to obtain an approximate three dimensional shape. Cloth and film laminates are also employed to improve stretch resistance and some sails are also reinforced with individual strands.
More recently, improved polymers have been developed, which, when formed into yarns, have very high stretch resistance. These include aramids, sold under the trademark xe2x80x9cKevlarxe2x80x9d, highly oriented, high molecular weight polyethylene, sold under the trademark xe2x80x9cSpectraxe2x80x9d, and specialized polyesters, sold under the trademark xe2x80x9cPentex,xe2x80x9d as well as others known in the art of sailmaking.
In the weaving process, the yarns pass over and under each other in a repeating pattern, which induces a certain amount of crimp in the yarn. Woven sailcloth cannot be made entirely from aramid yarns because the crimp reduces the desired stretch properties of the fabric and friction between yarns causes early failure. Thus, aramid and other cloths comprising low stretch yarns are made from low stretch yarns running in one direction and polyester yarns running in the other direction. Thus, the fabric is relatively weak in one direction, and the sailmaker designs sails in which the panels are arranged such that the strong yarns run in the direction of maximum load lines in the sail.
It is also known in the weaving industry that yarn crimp can be controlled in various ways. For example if fewer or lighter weight yarns are used in the fill direction than in the warp direction, the warp yarns will be relatively straight and uncrimped, and the cloth will have low stretch in the warp direction, but will have stretch in the fill direction.
While film and fabric laminates have greatly improved the low stretch properties of sails, there is a continuing need for improvements for woven sailcloth having high strength and low stretch in both the warp and fill directions.
The composite sailcloth of the present invention comprises at least three layers laminated together. One outer layer is a woven cloth in which high strength and low stretch yarns are oriented in the fill direction and relatively free of crimp. A central layer comprises a polymer film, preferably polyester. The third layer is a woven cloth in which the high strength and low stretch yarns are oriented in the warp direction. The assembly is laminated by applying a curable adhesive between both sides of the film and the woven layers.
The film layer may comprise a single sheet of film or a pair of films laminated together with reinforcing yarns extending at angles to the warp and fill directions of the woven cloth.
An additional warp oriented fabric may be laminated to the fill oriented layer using an additional layer of film, depending on factors such as desired basis weight and how the fabric will be used in the sail. Typical basis weights for fabrics of this nature will be in the order of five to twenty five ounces per square yard.